Add a hook run upon monitor configuration changes

* doc/lispref/frames.texi (Multiple Terminals): Document new
hook `display-monitors-changed-functions'.
* etc/NEWS: Announce new abnormal hook.

* src/keyboard.c (kbd_buffer_get_event): Handle
MONITORS_CHANGED_EVENT.
(syms_of_keyboard): New hook and defsyms.
* src/termhooks.h (enum event_kind): Add new event
`MONITORS_CHANGED_EVENT'.

* src/xterm.c (handle_one_xevent): Handle RRNotify and
RRScreenChangeNotify events.
(x_term_init): Select for RRScreenChange, RRCrtcChange and
RROutputChange.
* src/xterm.h (struct x_display_info): Improve RandR version
detection.

1 files changed, 9 insertions, 2 deletions

diff --git a/src/termhooks.h b/src/termhooks.h
index 08bde0aec0d..d7190e77362 100644
--- a/src/termhooks.h
+++ b/src/termhooks.h
@@ -31,7 +31,8 @@ struct glyph;
 
 INLINE_HEADER_BEGIN
 
-enum scroll_bar_part {
+enum scroll_bar_part
+{
   scroll_bar_nowhere,
   scroll_bar_above_handle,
   scroll_bar_handle,
@@ -301,8 +302,9 @@ enum event_kind
 #endif
 
 #ifdef HAVE_XWIDGETS
-  /* events generated by xwidgets*/
+  /* An event generated by an xwidget to tell us something.  */
    , XWIDGET_EVENT
+
    /* Event generated when WebKit asks us to display another widget.  */
    , XWIDGET_DISPLAY_EVENT
 #endif
@@ -349,6 +351,11 @@ enum event_kind
          positive delta represents a change clockwise, and a negative
          delta represents a change counter-clockwise.  */
   , PINCH_EVENT
+
+  /* In a MONITORS_CHANGED_EVENT, .arg gives the terminal on which the
+     monitor configuration changed.  .timestamp gives the time on
+     which the monitors changed.  */
+  , MONITORS_CHANGED_EVENT
 };
 
 /* Bit width of an enum event_kind tag at the start of structs and unions.  */